System of control.



G. H. HILL.

SYSTEM OF CONTROL.

nrmoulol nun In. as, 1901.

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G. H. HILL.

SYSTEM OF CONTROL.

APPLICATION nun Mums, 1907.

904,780. Patented Nov. 24, 1908.

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Witnesses: it Inventor:

George H.Hi|l,

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UNITED STATES PATENT OFFICE.

GEORGE H. BILL, OF SUHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SYSTEM OF CONTROL.

Specification of Letters Patent.

Patented Nov. 24, 1908.

Application filed March 23, 1907. Serial No. 364,061.

To all whom it"may concern:

Be it known that I, Grouch H. HILL, a citizen of the United States, residing at Schenectady, in the county of Schenectady and State of New York, have invented certain new and useful Improvements in Systems of Control, of which the following is a specification.

My invention relates to the control of electrical translating devices which are adapted to operate on both alternating and direct currents and has for its object to improve the same. i

The invention is particularly applicable to electric railways so equipped that the cars or train of cars operate on low potential direct current within city limits and on high potential alternating current throughout less thickly populated territory. In such a system it is necessary to provide step-down transformers on the cars or locomotives in order to reduce the potential of the alternating current to about the potential at which direct current is supplied. It. is also the practice to provide some means for changing the relative connections of the motor windings when passing from an alternating current to a direct current section, or vice versa; for example, the field windings of series motors or group of series motors are usually divided into two portions which are connected in parallel with each other for operation on alternating current and in series -with each, other during direct current operation. For these reasons-and also for the reason that when operating on direct current the most convenient way of controlling the current is by ,means of resistance, while on alternating current speed control can most conveniently be obtained by changing the point of connection between the motor and the current transformer,a large number of switch-mechanisms or circuit cont-rolling devices are necessary for making the various connections.

Specifically considered, the present invention consists of a multiple unit control system so arranged that a plurality of controllers of the separately-actuated contact type may be governed from anyone of a number of master controllers so as to connect a motor or motors eitherjo a source of alternating current or tqaasource of direct current;

to regulate the speed, when operating on direct current, by varying the resistance in the motor-circuit; and to regulate the speed, when operating on alternating current, by varying the point of connection to a transformer. The circuits are so arranged that the resistance and the resistance controlling contacts are made to serve the additional function of operating, during alternating current operation, to prevent open-circuiting or short-circuiting of the transformer during the shifting of the connection from one tap to another.

1n one of its aspects myinvention may therefore be regarded as comprising a novel alternating current and direct-current system of control wherein the parts are so organized and interrelated that a large number of control steps may be obtained, both for alternating current operation and for direct current operation, by means of a minimum number of switch mechanisms.

In a further aspect my invention may be regarded as a novel system of multiple unit control wherein a lurality of independent units are connected and controlled from a single master controller for operation on either alternating or direct current.

In a further aspect my invention may be regarded as a combined alternating current and direct current control system for a translating device, wherein the resistance used for governing the translatin device when operating on direct current 1s employed in making changes from one tap to another on a transformer during operationjon alternating current. v

In a still further aspect my invention may be considered as comprising a novel control system of the separatelyactuated contact type wherein a portionf of the contacts are used both for controlling "the resistance on direct current operation'and for effecting the changes in connection between the mo tors and the transformer during operation on alternating currents.

The various features of novelty characterizing my invention will be pointed out with particularity in the appended claims, but for afullunderstanding of my inven tion in its various aspects reference may be single car may be operated or a plurality of cars may be connected together and controlled in unison from the same master controller; Figs. 2 to 9 inclusive, are diagrams showing the manner in which the speed of the motors is controlled when operating on alternating current and when operating on direct current; and Fig. 10 shows a train of two cars equipped in accordance with my invention.

, In the drawing I have shown a fourmotor railway car e uipment; but it will of course be understoo that my invention is not limited to this particular arrangement but is applicable to any number of motors or other translating devices intended for other purposes than the propulsion of rail way vehicles.

Referring to the drawings, M to M represent two pairs of series motors such as are usually employed where it is intended that they shall operate both on alternating and direct current. In addition to the compensating windings, f to f, these motors ave main field windings F to F.

BS is a magnetically-actuated reversing switch of any usual type adapted to alter the relative connections between the armature and main field windings so as to re verse the direction of rotation of the motors.

E is an electromagnetically-actuated commutating switch which is so arranged that in one position it connects the main field windings of each air of motors in series with each other, w ile in its other position it connects these windings in parallel.

L is a trolley wire or other source of current su ply and T is a current collector adapted to engage with the trolley wire and carry current to the motors.

S and S are main switches, the switch S being adapted to close automatically when alternating current is being supplied and the switch S when the current is irect.

N is a stepdown transformer, preferably an auto transformer or com ensator,ada ted to be connected to trolley lly the switc S.

R is a resistance made up of any desired number of sections.

0 is a controller of the separately-actuated contact type arranged to connect the motors-either to variable points on the transformer, or to connect them directly to trolley in series with variable portions of re-.

sistance. In addition, the controller is arranged to connect the motors either in series or in series-parallel when operating on direct current.

master-controller. In the diagrammatic reprigsentation of the master-controller, the reevflgrsing switch. and the commutating switch,

A the switches to 11.

the small circles indicate stationary colilzu't fingers, while the rectangular segments ind l cate similarly-shaped contact-pieces ar ranged on the surface of a movable cylinder.

Q is a group of train wires to which the master controllers are connected in parallel. By means of these train wires the motors on a plurality of cars may be controlled simultaneously from any one master controller.

The motor controller consists of a plurality of line s\vitches,1, and 3. for connecting the motors to trolley, a series switch 4-. and two parallel switches 5 and (3. These switches come into play only when the motors are op crating on direct currents. Switches 7 to 11, inclusive, serve to connect the motors to different taps on theiransformer, these switches being used only when operating on alternat ing current. Switches 12 to 15, inclusive, when the motors are operating on direct current, control the amount of resistance in circuit with the motors; while during operation on alternating current these switches cooperate with the switches 7 to 11 to make the changes in the connections to the transformer.

U is a rela which controls the circuits of This relay is arranged to be energized only on alternating current, and therefore the switches 7 to 11 are cut out during direct current operation.

The arrangements of the various circuits can best be described in connection with the mode of o eration of the system. In the drawing, a l the parts are shown in the outof-running positions the conimutating switch E being shown in its direct current operating position and the reversing switch in its forward running position. Assume that the car illustrated is on a direct current section; then upon ringing the collector-shoe into engagement with the trolley wire, current flows through the primary of the small transformer it, through the actuating coil 8 in the switch S, to ground. The switch S closes and completes the connection between the trolley and the line switches 1, 2 and 3. Thereupon current flows through wire 16, through the actuatin coil 6 of the commutating switch, throng wire 18, through wire 19, to ground. The actuating coil of the commutating switch is therefore energized and the switch is thrown so as to make the pro er connections for operating the motors on irect current, unless it happens that, as illustrated, the commutating switch is already in this position. The chief function of the commutating switch indicated is to connect the main field windings of each group of motors in arallel for alternating current operation an in series for direct current operation. Therefore, in theposition of the oommutating switch illustrated, the field windin of each group are connected in series wit each other. It will be seen that the into its first operative position.

movable contact 20 of the commutating switch is now in engagement with two of the fixed contacts and completes a circuit from the wire 16 to wire 21, and thence to wire 22, which is connected to both of the master controllers The current for operating the several switches of the controller is received through this circuit.

If it be now desired to start the car the switch P is closed, the reversin switch is operated, and the master-control er is brought Current flows from the current collector, through the circuit previousl traced to wire 22 and thence through t e blow-out coil B O and switch P to contact 23 of the master-controller. From this point (assuming that the movable member 0 of the master reverser has'been moved to the right) current flows through the movable contacts of the controller, contact 24, thence through the master reversing switch to train wire 9, and from this train wire ciirrent flows through wire 25,

and thence through the actuating coil 1 of.

the reversing switch; and, if the reversing switch is not in the desired position, through the stationary contacts and connected movable contacts 26 and 27 of the reversing switch, through the auxiliary contact 1 connected with the main line switch 1, to ground. This causes the reversing switch to be brought into the position shown, and the circuit is interrupted at contacts 26 and 27 on the reversing switch; but a second circuit is completed by movable contacts 28 on the reversing switch and the cooperating fixed contacts so that the current now flows through the actuating coil of the reversing switch, through contact 28 of the reversing switch, through wire 29, and thence through the actuating coils of switches 1, 2, 3 and 4, through the auxiliary switch 6 associated with main switch 6, to train-wire (1 through the fixed contacts 30 and 31 and the cooperating movable contacts of the master controller, to ground.

The circuits heretofore traced are all control circuits, but now a main circuit may be traced fromtrolley, through the switch S, through line switches 1, 2 and 3, through resistance R, through conductor 32, through the armatures and compensating field windings f and f of the motors M and M through the reversirig switch, through the main field windings through the commutatin switch, through the main field windings through reverser contacts, through conductor 33, thence through switch 4, through the armatures and compensating field windings f and f of the motorsM and M, through reverser contacts through the field windings F through the commutating switch, and thence through the field windings F* and reversing switch, to ground;

' The motors, with the armature and field coils of each arranged in series, are now connected in series with each other and in. series with all of the resistance, as shown diagrammatically in Fig. 8.

As the master controller is turned. toward the right, contacts 34 to 37, inclusive, on the controller, engage successively with the cooperating stationary contacts, and current is caused to flow to train-wires g, g and g" in succession. This causes switches 12, 13, 14 and 15 to be closed, one after the other and, since each ofthese switches controls a section of the resistance, the resistance is cut out step-by-step until, when the switch 15 is closed, all of this resistance has been eliminated. It will be noted that the circuit which includes the actuating coil of switch 12 passes from train wire q through wire 38, thence through the auxiliary switch 7, associated with switch 7; whereby the switch 12 is prevented from closing unless the switch 7 is open. In the same way, the auxiliary switch 8*, associated with switch 8, controls the actuating circuit of switch 13; and the auxiliary switches 9 and 10 control the actuating circuits of switches 14 and 15. The purpose of this system of interlocks will be hereinafter ex lained. In turning the master controller tom the fifth to the sixth position, all of the circuits are interrupted, so that all of the controller switches open. In the sixth position of the master con' troller, train wire g, instead of train wire 9 as before, is connected to ground through the controller contact 31, and therefore the circuit for the series switch 4 is broken and the circuit which includes the actuating coils of the line switches 1 to 3, continues through the actuating coils of the parallel switches 6 and 5, through the auxiliary switch 4", associated with the series switch 4, to train wire 9, and thence through the controller, to ground. The motors, with the armature and field coils of each arranged in series, are now connected in parallel to the line with all of the resistance, exce t'the first section, in series therewith; the rst section of the resistance being cut out in the first parallel position throu h the energization of the ac tuating coil 0 switch 12, when the movable contact 39 on the master controller engages with the cotiperating fixed contact which is in electrical connection with train-wire q". This is the condition indicated in Fig. 9. Upon turning the master controller through its remaining operative ositions, the remainder of the resistance Ti the motors, with the armature and field coils of each arranged in series, are left connected in parallel with no extraneous resistance in circuit. I

In order to cause the car or train to move in the opposite direction, the master reversing switch is thrown toward the left, instead of toward the right, and then, except that is removed and the coil oi the reversing switch is energized and the motors reverscly connected,

the rest of the .uarrations just described take place as htto e iil specdnig up the motors tron: first serv u an all r "ance in circuit.

to full parallel with no l't iuli in circuit.

l'pon entering an whet-aiding current seciion, the current through the coil of the main switch 8 is cut down to such an extent by the action of transformer 12 that this switch re mains open; but the switch S, whose actuating coil is connected to the secondary of the small transformer. is caused to be closed, thereby connecting the main transformer to trolley. The connnuiating switch is now autoimitically thrown to the opposite posh lion irom that shown. so that the motors are autou'laiically connected up for proper operation on alternating current, namely, with the main field windings of each group of two motors in parallel with each other. The eration of the commutating switch to the a ternating current running position may conveniently be effected by connecting one terminal of the actuating coil 6 to ground and the other terminal to a tap on the compensator through a wire l0. hen the commutating switch is in its alternating current position. the movable contact ll. connects wires and El together in the same manner that contact connects together wires 16 and 21 when the com1nutatiu; switch is in its direct current position, that the current for ei'iergizing the switches of the main controller is now received from the compensator instead of directly from trolley, as before.

\Vhen it is desired to start the car, the master reversing switch is moved in one direction or the other as may be desired and the master controller is operated in exactly the same manner as when direct current is being supplied.

The switches l to (5 remain ldle (luring alternating current operation and, to prevent.

them from being closed, one terminal of each of the actuating coils r and r is grounded through contacts 42 to 46 on the commutating switch. Thus the current, after traversing the actuating coils of the reversing switch, flows directly to ground instead of through the actuating coils of switches 1. to G. A branch 47 extends from the wire l0 to each of the master controllers, through which, by means of eoi'iperating contacts 48 to 51, a c rcuit is completed to train-wire Q). Current flows from train-wire (1 through the actuating coil of relay U, through wire 52, and thence through contacts on the commutating switch, to ground. The contacts 50 and 51 on the master controller are of such len 11 that the circuit through the actuating 001 of the relay remains complete in all running positions of the controllerso that while the motors are operating on alternating current the relay U remains energized and has its movable contacts held in engagement with the fixed contacts. It will be noted that the relay is of a peculiar construction, namely, all of its movable contact members are electrically connected together and, since one of the fixed contacts is grounded, all of the wires which lead to the contacts of the relay are grounded when the relay is energized.

In the first running position of the master controller, train-wire g is energized by reason of the engagement of controller contacts 53 and 54, and current flows through the am tuating coil of switch 7, thence through the contacts of the relay, to ground. Switch 7 is therefore energized and closed, and wire 32, which leads to the motors, is connected to the lowest tap on the compensator. The conditions of the circuit are now as indicated in Fig. 2, namely, the motors are connected in parallel to the lowest tap on the transformer, and the main field windin s of each group of motors are also arranged in parallel with each other. To efl'eot increase 111 speed, the point of connection of the wire' 32 to compensator is changed so as to increase the voltage across the terminals of the motor. It is of course not desirable to open the motor circuit in changing from one speed to the other and therefore some means must be provided for preventing short circuit on the compen sator during the time when connection is maintained at two ditferent taps. To this end I make use of the main resistance and the resistancecontrolling switches so that before the circuit is broken at one tap on the compensator a resistance is connected between that tap and the next succeeding tap, whereby the motors are connected directly to one of the taps, and to the other through a resistance. The parts are so arranged that the low-voltage connection is then interrupted and the resistance cut out, leaving the motors connected directly to the compensator, but at a point of higher voltage than before.

Fig. 2 shows the connections when the controller is in its first running position, and Fig. 5 the connections when the controller 15 in its second running position.

Figs. 3 and 4 show the transition steps which are made While the controller is moving from the first to the second position. It will be seen that the contacts on the master controller are so arranged that in moving the controller from the first position to the second position, train-wire g is energized before train wire 9 is deener ized; thus switch 8 is closed before switch is opened. Consequently, for an instant, the circuits leadin from the transformer are as indicated in Fig. 3, namely, the motors are connected directl to the left-hand tap on the commutator t rough switch 7 and through the second tap on the left through switch 8 and a section of resistance B. When the contact; 53 on the master controller has i open and the switch 15 closes.

moved fully out of engagement with co- When operating on alternating curt-:nt, the

operating contact 54, train wire 9 is do energized and switch 7 opens. The connections are now as shown in Fig. 4. and the motors are; cpnnected to the second tap on the transfo'r'ii'l er through a section of resistance. As soon as the switch 7 opens, it closes its auxiliary switch 7* and current passes from the train wire gf through this auxiliary switch, and thence through the actuating coil of switch 12, so that switch 12 closes and short-circuits the section of resistance, as indicated in Fig. 5. Thus the motors ale connected directly to the second tap on the transformer without the intervention of any extraneous resistance. In the same way in moving from second to third position of the controller train-wire g isenergized before the trainq ire is deenergized, and therefore switch 9 closes before -switches 8 and 12 open. This is the condition indicated in Fig. 6. Thereafter, switches 8 and 12 open, leaving the motors connected to the third tap of the transformer .in series with two sections of resistance.

\Vhen this occurs the actuating circuit for switch 13 is completed through the auxiliary switch 8, and switch 13 closes and shortcireuits the resistance. The condition is now that shown in Fig. 7, namely, the motors are connected directly to the third tap on the transformer. In this same way in moving to the fourth running position, the switch 10 is closed, and switchcs 9 and 13 open and then the switch 14 is closed. In moving the controller from the fourth to the fifth position, the switch 11 closes before the switches 10 and 14 open, then the switches 10 and 14 It will thus be seen that the voltage across the terminals of the motors is gradually increased without.

opening the motor circuit and without in any way endangering the transformer. Eurthermore, this is effected without the use of any switches or devices which are not useful when operatin on direct current, exoept; the several switches 7 to 11, inclusive, which are connected directly to the taps of the transformer. By thus using the main resistance and a group of switches both for alternating current operation and direction current operation, the amount of apparatus required is reduced to a minimum wlthout interfering in any way with the proper operation of the systemon either current.

I have also shown at M a motor such as -an air-pump motor, together with a relay W, which is energized on direct current, by reason of being connected to wire 16 so as to change the connections of the motor windlngspassing from one section to another. It W1 1 e seen that when the rela W is energized, current flows from trofley through wire 16', wire-60, and through the armature and fieldwindings in series with each other.

relay being deenergizcd, current flows from one of the taps on the compensator through wire (El and thence through the armature of the motor M and the two field windings 62 and 63 connected in parallel. This feature forms no part of the present invention but illustrates a convenient manner in which the auxiliary motors such as pump motors and the like may be controlled so as to operate satisfactorily on either current.

The switches or contacts 715 which operate on both direct and alternating current may be of any suitable design and may con-- venicntly take the form disclosed in my ap plication Serial No. 294,503, filed January 4, 1906; but the switches or contacts 1 to 6, being intended to operate only on direct current, may be of any of the well known types now in use in direct current control systems.

While I have described in detail vcntjon embodied in a single preferred form, I do not desire to be limited to the particular form illustrated or described, since in its broader as ects my invention may take various other fhrms; and furthermore many of the features of invention, while coiiperating advantageously to produce an efficient system as a whole, may yet be used independently of each other, since they contain useful and novel elements of construction and organization and have novel functions which are applicable to situations apart from those wherein all of the features are combined into a single whole.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. In a system of control, a translatin device, a main controller having separate a ternating-current and direct-current governin means for said device, and a master contro ler for said main controller.

2. In a system of control, a translating dc vice, a controllingdevice for alternatingcurrent operation, a controlling-device for direct-current operation, and a master con troller for governing both of said controlling devices.

3. In a system of control, a motor, a motor-controlling device for alternatingcurrent operation, a motor-controlling device for direct-current operation, and a master controller for overning the action of both of said control ing devices. 7

4. In a system of control, a motor, a speed controlling device for use on alternatingcurrent, a second speed controlling device for use on direct-current, switch-devices for governing said controlling devices and a master controller for governing said swifleh devices.

5. In a system of control, a translating device,'a transformer, a resistance, switchabvices for connecting said translating device to the transformer for alternating current my inoperation, switch devices for connecting the translating device to a source of supply with said resistance in circuit for operating on direct currents, and a masteccontroller for governing the operation of the said switchdevices. 1

6. In a system of control, a translatin device, a transformer, a resistance, switc -devices for connecting said translating device to variable points on the transformer for operation on alternating current, switch devices for connecting said translating device to a source of current with variable portions of said resistance in circuit for operation on direct current, and a master controller for governing said switch devices. Y

7 In a system of motor control, a motor, a transformer, a resistance, a motor controller of the separately-actuatcd contact type having contacts for connecting the motor to variable taps on the transformer and other contacts for connecting the motor to a source of supply with variable portions of the resistance in circuit, and a maste1'controller for governing the act ion of all of said contacts.

8. In a control system, a controller of the separately-actuated contact type' having a set of alternating current contacts and a. set of direct current contacts, a master controller, and means for causing said master controller to operate selectively on said sets of contacts so as to cause a contact in one set or the other to be actuated when the master controller is in a given position, according as the current is alternating or dlrect.

9. In a train-control system, a plurality of motor controllers each having alternatingcurrent and direct-current contacts, a master controller, and a single set of train wires connecting said master-controller to allof said motor controllers.

10. In a system of control, a translating device, a transformer, a resistance, and a controller arranged to connect said translating device to variable points on the transformer when operating on alternating-current and to a source of current with variable portions of said resistance in circuit for operation on direct-current, said controller including means for connecting portions of said resistance in a branch circuit between the translating device and one tap on the transformer before connection is broken between the translating device and another tap on the transformer.

11. In a system of control, a translating device, a controller having contacts for governing the operation of said translating device on alternating current and other contacts for governing the operation of said translating device on direct current, electromagnetic actuating ans for said contacts, a commutating SWItLill for va ing the circuit connections for said trans ating device,

and means amociated with said commutatin switch for controlling the circuits of said actuating means to cause said contacts to be selectively actuated accordin as the current which is being supplied is irect or alternating.

12. In a s stem of control, a motor, a motor contro ler having contacts for controlling the operation of said motor on alternating current and other contacts for controlling the operation of the motor on direct current, electromagnetic actuating means for said contacts, a relay for controlling the circuits of the actuating means for one set of contacts, a commutating switch arranged to vary the relative connections of the motor windings, and contacts on said commutating switch for controlling said relay;

13. In a system of control, a motor, a motor controller having a plurality of contacts arranged to control the operation of the motor on alternating current and other contacts for controlling the operation of the motor on direct current, a reversing switch, actuating means for said contacts and for said reversing switch, control circuits for the actuating means for the reversing switch arranged to energize also the actuating means for one of said sets of contacts, a commutating switch for changing the relative connections of the motor windings, and contacts on said commutating switch 'for completing the circuit through the reverser actuating means independent y of the actuating means of said latter set of contacts.

14. In a system of control, a plurality of groups of series motors, and a combined alternating and direct current controller arranged to connect the groups of motors in parallel with each other with the field windings of one motor in each group connected in parallel with the field windings of the other motor in that group for operation on alternating current and or connecting the grou s of motors first in series and then in para lel for operation on direct current, the armature and field windings of each group being arranged in series during operation on direct current.

15. In a system of control, a motor, a plurality of contacts for controlling the operation of the motor on direct current, a plurality of contacts arranged to operate only on alternating current, actuatin means for said contacts, a master control er, and a. singleset of connections between the master controller and the actuating means for said contacts. I

16. In a systemof control, a. motory'a set I of contacts arranged to be actuated for con- .125 trolling the operation of the motor only on alternating current, a second set of contacts arranged to be actuated to control the-.operation of the motor on direct current, a mastcr controller, a single set of connections 130 from the master controller to the actuating means for both sets of contacts, and means associated with the set of alternating current contacts for automatically causing the operation of the other set of contacts.

17. In a s stem of control, a motor, a set of contacts or controlling the operation of the motor on alternating current, a second set of contacts for controlling the operation of the motor on direct current, actuating means for said contacts, a master controller, a single set of connections from said master controller to the actuating means of both contacts, a relay for governing the circuits of the actuating means for one set of contacts, and means controlled by the latter con tacts for controlling the actuating circuits for the other contacts.

18. In a system of control, a motor, a group of contacts arranged to control the operation of the motor on alternating current, a similar grou of contacts arranged to control the operation of the motor on direct current, a master controller. and connections between the master controller and the actuating means for said contacts so arranged that the operation of the master controllcr causes the contacts of one group or the ot her to he actuated according as the current supply is alternating or direct, and means associated with one of said groups of contacts to cause the automatic actuation of the contacts of the other group.

l9. In a tom of control, a plurality of motors. a rcs stance, a transformer, a group of contacts arranged to connect the motors to (liii'crenl points on the transformer in two groups arranged in parallel for operation on alternating current and to a source of current supply in series and then in series parallel with different amounts of said resistance in circuit for operation on direct curtroller and connections so arranged that upon the operation of the master controller from one position to the next the translating device is first connected to one tap on the transformer and then to a second tap through said resistance and the connection to the first tap is then interrupted and the resistance cut out.

21. In a system of control, a motor, a transformer, a resistance, a series of switches for connecting the motor to different points on the transformer for operation on alternating current, a second series of switches for varying the amountof said resistance in the motor circuit when operating on direct current, a master controller, and connections so arranged that upon the operation of the master controller from one running position .to another the motor is first connected to one tap on the transformer, a resistance controlling switch is operated to connect the motor to a second tap on the transformer through a portion of the resistance and finally the connection to the first tap is interrupted and the resistance eliminated from the motor circuit.

In Witness whereof, I have hereunto set my hand this 21st day of March. 1907.

GEORGE H. HILL. \Vi tnesses BENJAMIN B. HULL. IIELEN Onronn. 

